/**
 * @description:下雪效果
 * @date：2025.07.15
 */
export default class SnowEffect {
  snowSize: number | undefined;
  snowSpeed: number | undefined;
  viewer: Cesium.Viewer;
  snowStage?: Cesium.PostProcessStage;

  constructor(
    viewer: Cesium.Viewer,
    options: { snowSize: number; snowSpeed: number }
  ) {
    if (!viewer) throw new Error('no viewer object!');
    options = options || {};
    this.snowSize = Cesium.defaultValue(options.snowSize, 0.02); //最好小于0.02

    this.snowSpeed = Cesium.defaultValue(options.snowSpeed, 60.0);
    this.viewer = viewer;
    this.init();
  }

  init() {
    this.snowStage = new Cesium.PostProcessStage({
      name: 'czm_snow',
      fragmentShader: this.snow(),
      uniforms: {
        snowSize: () => {
          return this.snowSize;
        },
        snowSpeed: () => {
          return this.snowSpeed;
        },
      },
    });

    this.viewer.scene.postProcessStages.add(this.snowStage);
  }

  destroy() {
    if (!this.viewer || !this.snowStage) return;
    this.viewer.scene.postProcessStages.remove(this.snowStage);
    this.snowStage.destroy();
    delete this.snowSize;
    delete this.snowSpeed;
  }

  show(visible: boolean) {
    this.snowStage!.enabled = visible;
  }

  snow() {
    return `
      uniform sampler2D colorTexture;
      in vec2 v_textureCoordinates;
      uniform float snowSpeed;
      uniform float snowSize;
      float snow(vec2 uv,float scale) {
        float time=czm_frameNumber/snowSpeed;
        float w=smoothstep(1.,0.,-uv.y*(scale/10.));if(w<.1)return 0.;
        uv+=time/scale;uv.y+=time*2./scale;uv.x+=sin(uv.y+time*.5)/scale;
        uv*=scale;vec2 s=floor(uv),f=fract(uv),p;float k=3.,d;
        p=.5+.35*sin(11.*fract(sin((s+p+scale)*mat2(7,3,6,5))*5.))-f;d=length(p);k=min(d,k);
        k=smoothstep(0.,k,sin(f.x+f.y)*snowSize);
        return k*w;
      }
      out vec4 vFragColor;
      void main(void){
        vec2 resolution=czm_viewport.zw;
        vec2 uv=(gl_FragCoord.xy*2.-resolution.xy)/min(resolution.x,resolution.y);
        vec3 finalColor=vec3(0);
        //float c=smoothstep(1.,0.3,clamp(uv.y*.3+.8,0.,.75));
        float c=0.;
        c+=snow(uv,30.)*.0;
        c+=snow(uv,20.)*.0;
        c+=snow(uv,15.)*.0;
        c+=snow(uv,10.);
        c+=snow(uv,8.);
        c+=snow(uv,6.);
        c+=snow(uv,5.);
        finalColor=(vec3(c));
        vFragColor=mix(texture(colorTexture,v_textureCoordinates),vec4(finalColor,1),.5);
      }
    `;
  }
}
